In recent years rising labor and material costs have prompted industrial investigation of materials which may be suitably substituted for those traditionally employed. Such investigations have suggested the substitution of thermoplastic materials for uses formerly employing leather and cloth because these materials are often less expensive and easier to form into a desired article than leather or cloth. As a result, the shoe and other industries using large amounts of leather and/or cloth have increasingly attempted to substitute thermoplastic materials for their traditional counterparts.
Commercial acceptance of thermoplastic materials as substitutes for traditional materials has at times required that the thermoplastic materials be processed to resemble the displaced traditional materials. In the shoe industry, for example, heat softening thermoplastic materials to weldingly combine the materials with seams is substantially functionally equivalent to a stitched seam but is not generally commercially acceptable because of appearance. However, welded seams are usually easier to form than stitched seams. Thus, cost reductions and commercial acceptance could be achieved if welded seams were made to resemble stitched seams. Embossing thermoplastics with a die having desired features and heat and pressure can provide this resemblance. Similarly, other surface patterns and characteristics could be embossed on thermoplastic material to cause the thermoplastic materials to resemble traditional materials, thereby achieving still further cost reductions and improved commercial acceptance of the thermoplastic materials.
When traditional articles are comprised of leather or cloth, the thread of stitches or decorative bits of leather or cloth employed is frequently of a different color from adjacent portions of the material of the article. Embossing thermoplastic materials has not hitherto satisfactorily provided a two-color appearance to the material and in this respect failed to duplicate the appearance of traditionally made articles.
Prior attempts to provide two-color embossing have been made. One attempt to achieve two-material and/or two-color embossure of thermoplastic materials requires the painting, doctoring or injecting of a second material into portions of a die for embossing the thermoplastic material where it is desired to have the distinguishable second material and/or color. Painting and doctoring are difficult to achieve with accuracy and require skilled hand labor, especially for small areas to be inserted in the embossing die.
Another approach to achieve two-material and/or two-color embossing requires fitting the die with a rod or strip of thermoplastic material to be weldingly combined with the workpiece when the workpiece is embossed. Where the pattern to receive the second color is small or complex, the latter technique requires skilled hand labor and considerable time to appropriately fit the second layer into the embossing die.
Still another effort to achieve two-material and/or two-color embossure requires doctoring a second material into bas-relief features in the workpiece. The features may be molded in situ with the workpiece or later punched or flow-molded into the workpiece by a die for that purpose. In addition to the problem of precisely filling small features, this procedure has the problem of cleaning the second material from the workpiece surface adjacent the feature, particularly if that surface is uneven, for example as in suede.